Filaments with Affinity Binding and Wet Strength Can Be Achieved by Spinning Bifunctional Cellulose Nanofibrils

We demonstrate benzophenone (BP) conjugation via amine-reactive esters onto oxidized cellulosic fibers that were used as precursors, after microfluidization, of photoactive cellulose nanofibrils (CNF). From these fibrils, cellulose I filaments were synthesized by hydrogel spinning in an antisolvent followed by fast biradical UV cross-linking. As a result, the wet BP-CNF filaments retained extensively the original dry strength (a remarkable ∼80% retention). Thus, the principal limitation of these emerging materials was overcome (the wet tensile strength is typically <0.5% of the value measured in dry conditions). Subsequently, antihuman hemoglobin (anti-Hb) antibodies were conjugated onto residual surface carboxyl groups, making the filaments bifunctional for their active groups and properties (wet strength and bioactivity). Optical (surface plasmon resonance) and electroacoustic (quartz crystal microgravimetry) measurements conducted with the bifunctional CNF indicated effective anti-Hb conjugation (2.4 mg m^-2), endowing an excellent sensitivity toward Hb targets (1.7 ± 0.12 mg m^-2) and negligible nonspecific binding. Thus, the anti-Hb biointerface was deployed on filaments that captured Hb efficiently from aqueous matrices (confocal laser microscopy of FITC-labeled antibodies). Significantly, the anti-Hb biointerface was suitable for regeneration, while its sensitivity and selectivity in affinity binding can be tailored by application of blocking copolymers. The developed bifunctional filaments based on nanocellulose offer great promise in detection and affinity binding built upon 1D systems, which can be engineered into other structures for rational use of material and space.